We assume that all biological processes come to an end when we die, but new research shows that many genes remain active for up to four days following clinical death. These zombie genes can’t bring a person back to life, but this discovery has serious implications for forensics and organ donor recipients.

A pair of new studies, both of which are still undergoing peer review, are teasing our conceptions of death and what goes on in our bodies after we die. University of Washington biologist Peter Noble and his pals have shown that certain parts of the body remain active even after the rest of it has come to a grinding halt. In future, these insights could be used by scientists who are seeking to improve the way that donated organs are preserved, and by forensic investigators seeking to determine when a person was killed.

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As Mitch Leslie points out in Science Magazine, previous work on human cadavers demonstrated that some genes remain active after death, but we had no idea as to the extent of this strange phenomenon. By analyzing the tissue of recently deceased animals, Noble and his colleagues managed to pinpoint hundreds of genes that were still functioning in the days—yes days—following death. If the same thing applies to us—and there’s no reason to believe it doesn’t—it could change the way we perceive the recently deceased and how we define death.

In the first of the two studies, the researchers sought to determine which genes out of about a thousand might still be functioning in zebrafish and mice in the immediate days following death. To their surprise, the researchers found that hundreds of genes sprung back to life. Not only that, the activity of some of these genes actually increased. Most of these genes eventually gave up after about 24 hours, but some remained active for as much as four days after death. That’s surprising, to say the least.

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The majority of these zombie genes were not random in terms of function. Each of them play an important role when an animal experiences some kind of trauma or illness. For example, some genes that were ramped up are responsible for stimulating inflammation and the immune system as well as for countering stress. Some genetic activity, like a gene that’s responsible for embryonic development, baffled the scientists. Noble suspects that this gene becomes active because the cellular environment in dead bodies must somehow resemble those found in embryos.

Importantly, several genes that promote cancer also became active. This may explain why many organ donor recipients develop cancer. This tidbit of information could help scientists develop better methods of organ preservation prior to transplantation.

The second study, also co-authored by Nobel, shows that similar assessments of postmortem genetic activity could be used in criminal and civil investigations. Forensic teams could take genetic samples at murder scene, for example, to get a better estimate of time of death.

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As noted, these two papers have yet to appear in a peer-reviewed journal, and the genetic evaluations were not performed on human cadavers. Further research will be required before we draw too many conclusions about these fascinating studies.